A general requirement of such couplings is that the respective halves of the coupling each incorporate a valve that can be opened when the coupling halves are properly connected one to the other, and, which must be moved to a fully closed condition before the respective halves of the coupling can be separated one from the other. This is in order that fluid material present in the respective hoses, pipes or nipple, and which probably is under pressure, shall remain trapped within the hose, pipe or nipple and restrained against spillage upon separation of the coupling halves. In some circumstances, such as the top filling of storage tanks, only one of the couplings may be required.
The provision of such valves, while relatively simple in basic concept, poses unusual problems in the reduction to practice of that concept. Only the smallest possible amount and preferably zero of the flammable or noxious liquid can be permitted to remain trapped between the respective valves when the valves are in their closed position, in that the trapped liquid will be released to atmosphere or spilled onto the ground upon the separation of the coupling halves.
A desirable requirement is that the interconnecting members of the respective coupling halves be identical with each other in all respects, in order that any one coupling half can be connected to any other coupling half or to a corresponding connecting nipple, i.e., that the coupling halves be "sexless" or hermaphroditic in all respects, to the total avoidance of male only coupling halves and female only coupling halves. Dissimilar coupling halves carry the penalty that only one selected of a hose can be connected to a corresponding selected one end of another hose, or, to a corresponding selected nipple. Reversal of the ends of a hose having dissimilar coupling halves at its respective ends would preclude the assembly of that hose to another hose or nipple having interconnections corresponding with that at the said one selected end of that hose.
Preferably, some form of locking mechanism is provided that precludes separation of the coupling halves until such time that the respective valves have been moved to their fully closed position, and which permits separation of the coupling halves only when the respective valves have reached their fully closed position.
A coupling that goes a long way to meeting these conditions is the one disclosed in U.S. Pat. No. 4,438,779, to Allread, issued Mar. 27, 1984.
The coupling of that patent fully meets the conditions of identical coupling halves that are locked in assembled condition until each of the contained valves separately are moved fully to their closed position, but only partially meets the requirement that the smallest possible amount of flammable or noxious liquid shall remain trapped between the respective valves upon closure of the valves.
In that patent, ball valves are employed as the respective closure valves, the ball valves each being rotatable about an axis perpendicular to the longitudinal axis of a cylindrical port extending through the associated ball.
Provision is made for the sealing of the respective coupling halves to each other and to the associated ball valves on diameters that closely approximate the diameter of the through port in the respective balls. However, in order to permit closure of the ball valves, they must be positioned with their centers spaced by a distance which is not less than one half the combined diameters of the ball valves. This is in order to permit rotation of the respective ball valves to their closed position.
Such a construction, however, results in a void in the form of a double meniscus between the respective ball valves when in their closed position, the meniscus having a diameter that is the same as or greater than the diameter of the through port in the respective ball valves, and having opposite concave curvatures represented by the respective outer spherical faces of the respective valves.
As will be appreciated, the greater the diameter of the through ports and thus of the ball valves, then, the greater will be the contained volume of the meniscus, and, the volume of the liquid that is released to atmosphere or spilled upon separation of the coupling halves. For a typical coupling of 1.5 inches bore diameter, this can result in the release to atmosphere and spillage of two or more fluid ounces of the flammable or noxious liquid, a condition which obviously is to be eliminated if at all possible, when handling flammable, toxic, or noxious materials.
An alternative form of dry break coupling has been disclosed in U.S. Pat. No. 4,271,165, Galloway et al. issued June 9, 1981 which overcomes to the greatest possible extent the problems of spillage upon separation of the coupling halves, but, only at the expense of imposing a very considerable resistance to fluid flow through the assembled coupling, and, the requirement to provide dissimilar and complex male and female coupling halves.
In this patent, poppet valves are provided within the respective coupling halves. The poppet valves are supported for movement axially of the fluid flow passages. After the closure and locking of the coupling, one of the poppet valves is manually moved axially in a direction to displace the other poppet valve axially, and, to open fluid flow passages extending through the first poppet valve.
The poppet valves have planar faces that engage one another. Thus, theoretically, zero volume is left between the mating faces.
However, this advantage is obtained only at the combined disadvantages of providing dissimilar coupling halves, that imposing a very high frictional drag on the fluid flow and throttling of the fluid flow as it passes through the coupling, and that of providing couplings of considerable size, weight, and manufacturing cost.
Throttling of the fluid flow as it passes through the coupling results in an increase in transfer time and in turn produces a requirement for pumps of increased power for the transmission of the flammable or noxious fluid, and, requires seals in the coupling halves that are capable of withstanding the enhanced pumping pressure.
Another form of dry break coupling is disclosed in Cooper, U.S. Pat. No. 3,106,223, issued Oct. 8, 1963. Cooper, however, cannot meet the industry standard requirement that only a 90.degree. turn of the operating shaft of the valve is required to move the valve between fully opened and fully closed positions. In the Cooper construction it is required that the operating shaft of the valve be rotated through a full 180.degree. in order to move the valve between a fully opened and a fully closed position. Thus, in Cooper, the valve actuating lever, if provided, will extend either transverse to, or, in line with the flow path of the coupling, without regard to whether the valve is opened or closed.